update some tips

session/README.md

@@ -81,17 +81,21 @@ Writing a provider is easy. You only need to define two struct types
 Maybe you will find the **memory** provider as good example.
 
 	type SessionStore interface {
-		Set(key, value interface{}) error // set session value
-		Get(key interface{}) interface{}  // get session value
-		Delete(key interface{}) error     // delete session value
-		SessionID() string                // return current sessionID
-		SessionRelease()                  // release the resource
+		Set(key, value interface{}) error //set session value
+		Get(key interface{}) interface{}  //get session value
+		Delete(key interface{}) error     //delete session value
+		SessionID() string                //back current sessionID
+		SessionRelease()                  // release the resource & save data to provider
+		Flush() error                     //delete all data
 	}
 	
 	type Provider interface {
 		SessionInit(maxlifetime int64, savePath string) error
 		SessionRead(sid string) (SessionStore, error)
+		SessionExist(sid string) bool
+		SessionRegenerate(oldsid, sid string) (SessionStore, error)
 		SessionDestroy(sid string) error
+		SessionAll() int //get all active session
 		SessionGC()
 	}